This invention relates generally to the manipulation of light carried by optical fibers. More particularly, the present invention relates to stabilizing reflected light propagating along optical fibers.
In recent years, the use of optical fibers has become increasingly widespread in a variety of applications. Optical fiber probes have been found to be especially useful for analyzing materials by employing various types of light-scattering spectroscopy.
Optical fibers offer numerous advantages over other types of source/detection equipment. In short, the fiber provides a light conduit so that the source-generating hardware and the recording apparatus are stationed independently of the subject under investigation and the point of analysis. Thus, analyses are conducted remotely in otherwise inaccessible locations. Previously unattainable information is acquired in situ, often in real-time. This capability is sought in numerous industrial, environmental, and biomedical applications. The laboratory is moved on line in the industrial realm, to the field in the environmental sector, and in vivo in the biotechnical arena. Additionally, hardware and measurements are more robust, quicker, less intrusive, more rugged, less costly, and many other advantages are realized.
Light Scattering Spectroscopy
While transmission spectroscopy analyzes light passing through a substance, lights-scattering spectroscopy entails illumination of a measurand and analyzing light that is scattered at angles relative to the incident source. The photon-matter interactions of the scattering events may be either elastic or inelastic. In an inelastic event, a photon""s energy (wavelength) changes as a result of the light-matter interaction. In an elastic event, a photon""s energy (wavelength) does not change. Absorption, the phenomena in which a fraction of photons are entirely absorbed, also plays a role in light-scattering spectroscopies. Raman, diffuse, reflectance, and fluorescence spectroscopies are of particular interest as they relate to vibrational and nonvibrational photonic responses of a material.
The Raman effect describes a subtle light-matter interaction. Minute fractions of light illuminating a substance are Raman-scattered in random directions. Raman-scattered light is color shifted from the incident beam (usually a laser). The color (frequency) shifts are highly specific as they relate to molecular bond vibrations inducing molecular polarizability changes. Raman spectroscopy is a powerful technique for chemical analysis and monitoring. The resulting low light levels require sophisticated, expensive instrumentation and technical complexity. Suitable technology and products for on-line analysis of processes and environmental contaminants are just becoming available.
Specular reflectance relates to a surface""s mirror-like aspects. Diffuse reflectance relates to light that is elastically scattered from a surface of material at diffuse angles relative to the incident team. For example, a projector screen diffusely reflects light while a glossy, new waxed car has a high specular component. Diffuse reflectance spectroscopy is important for chemical analysis as well as measuring visual perception. Among other things, it is based on particulate-scattering and absorption events.
Fluorescence relates to substances which absorb light at one wavelength then re-emit it at a longer wavelength as a result of electronic transitions. As an example, a xe2x80x9chighlighterxe2x80x9d felt-tip marker appears to xe2x80x9cglowxe2x80x9d green as it absorbs blue and ultraviolet light then emits it as green. Fluorescence provides a powerful technique for chemical monitoring.
Raman spectroscopy is a well-established laboratory technique and is generally recognized as having enormous potential for on-line monitoring and sensing. With the advent of stable lasers, cheap computing power, efficient detectors, and other new technological advancements, Raman spectroscopy is primed for widespread industrial monitoring deployment. In addition to process control monitoring, it will be utilized in specialized monitoring and sensing devices ranging from neuroimaging to environmental monitoring, to in vitro and in vivo medical testing.
Raman spectroscopy involves energizing a sample with a high-power, narrow-wavelength energy source, such as a laser. The laser photons induce low intensity light emissions as wavelengths shift from the laser""s. The Raman effect is an elastic scattering of photons The emitted Raman light is collected and analyzed with a specialized instrument.
The spectral positions (colors) of the shifts provide fingerprints of the chemicals in the sample. Thus, Raman spectroscopy provides a means for chemical identification. The intensity of the shift (the spectral peak height) correlates to chemical concentration. Thus, a properly calibrated instrument provides chemical content and concentration. In practicality, Raman spectroscopy is technically complex and requires sophisticated, expensive instrumentation.
Raman spectroscopy is well suited to aqueous-based media without sample preparation. From this standpoint, it is an ideal tool for process control medical testing and environmental applications. Thus, Raman spectroscopy has great potential for real-time monitoring and is being vigorously pursued.
The basic concept for a probe-based, on-line Raman instrument is simple. Laser light is directed down an optical fiber to a remote probe. The laser light exits the fiber and illuminates the sample medium. Another fiber picks up the Raman-emitted light and returns it to the instrument for analysis.
In practicality, the engineering challenges for a robust physical probe implementation are substantial. In addition to the optical performance expected by laboratory instruments, a probe must be hardened to withstand extreme physical and chemical conditions. Optical characteristics must also remain constant as dynamic conditions change.
Optical aspects of probe engineering require particular design finesse. The Raman effect involves very weak signals. Raman emissions may be one trillionth as intense as the exciting radiation. Subsequently, the probe must be incredibly efficient in collecting and transmitting Raman-emitted light. And, the signal must not be corrupted by extraneous influences. As an example of the sensitivity, Raman instruments typically feature cosmic ray filters. The mechanisms identify and discard measurement data samples influenced by passage of a single cosmic ray photon through the detector.
A phenomenon known as the silica-Raman effect has proven especially troublesome for those engaged in remote Raman spectroscopy. As laser light is transmitted over optical fibers, a subtle light-matter interaction inherently occurs. The laser light and the silica in the glass fiber interact generating xe2x80x9csilica-Ramanxe2x80x9d light. The extraneous silica-Raman light becomes wave guided in the fiber and hopelessly mixed with the laser light. The purity of the laser light is corrupted. Fiber fluorescence causes similar problems.
Remote Raman spectroscopy employs optical fiber between the base instrument and the remote probe or process interface. Optical fiber delivers laser light from its source to the probe. Separate fiber returns sensed light from the probe to an instrument for analysis. In both delivery and return, undesirable silica-Raman light travels in the fibers concurrently with desirable laser and sensor light. A major obstacle in fiber-optic-based Raman spectroscopy has been in separating the desirable light from the undesirable silica-Raman light.
In addition to the undesirable Silica-Raman light, another problem exists with the separate fiber or fibers that return reflected light from the probe to the instrument for analysis. Specifically, problems arise when dispersive instruments are used to analyze the collected reflected light. Various light processing units or instruments require specific fiber input configurations. While non-dispersive light instruments typically accept light input via optical wave guides having a circular geometry, dispersive light instruments or light processing units typically perform best when the input or optical wave guide is shaped into a narrow rectangle. Such an input configuration is often referred to as a slit. This slit geometry makes it difficult to provide collection wave guides that can readily adapt to a specific configuration without degrading the quality and quantity of the collected reflected light energy.
Further, for the configurations in which ring fibers are employed to collect light, the light from these fibers can vary in intensity from one fiber to another due to either imperfections along individual fibers or due to relative different intensities at the actual collection site on a sample. Many dispersive light processing units or instruments, such as spectrographs, require the collected reflected light at the slit input to be of a substantially even intensity in order to enhance the analysis of the reflected light.
Accordingly, a need in the art exists for a method and system for stabilizing reflected light that is fed into a dispersive light processing unit, such as a spectrograph. There is a further need in the art for a method and system for stabilizing reflected light in addition to properly shaping the collected light wave guides to substantially match the input geometry configuration of a light processing unit.
Drug Development and the Long Felt Need for in-vivo Chemical Analysis
Drug development starts with the compilation of a list of candidate compounds. These may be derived from any number of methods ranging from extracts of natural products to automated development and design techniques. Combinatorial chemistry is one of these techniques. Currently, the technique is very time consuming. A need in the art exists for a method and system that can enhance the drug development process through real-time in vivo chemical analysis which, in turn, will decrease the amount of time for tracking the effects that drugs have on organisms. But to better appreciate this need for in-vivo chemical analysis, a discussion of the current state of drug development is necessary.
Drug Development Through Combinatorial Chemistry
Combinatorial chemistry is the synthesis of large numbers of compounds that are systematic variants of a chemical structure. Traditionally, searching for new chemicals meant assembling molecules one at a time in individual test tubes. Over decades, shelves of created compounds have been generated and collected and later are screened again, one at a time, against a molecular target; it is a tedious process. Combinatorial chemistry shifts compound design from a one-molecule-at-a-time approach to automated parallel synthesis. Starting with a useful compound or molecule, robotics may be used to spin a lead into hundreds of thousands of chemical variations. The resulting chemical diversity boosts the chance that a new compound will usefully react with a molecular target.
In the last 15 years, combinatorial chemistry has expanded from peptides to organic, organometallic, inorganic and polymer chemistry. Industrial applications not only include pharmaceuticals but also electronic materials; catalysts; polymers; pigments for plastics, coatings and fabrics; advanced materials; and agricultural chemicals. The initial mechanism of drug action is the specific binding or docking of a portion of the drug candidate to a receptor site. This action is conceptually similar to that of many catalysts in promoting chemical reactions, particularly polymerizations. So, it is not surprising that combinatorial chemistry is being used to synthesize catalyst candidates. Similarities also exist between material science and drug discovery. The properties of materials are not always predictable from the structures, and synthesis is complex. Material scientists and researchers need better ways to manage arrays of materials and identify chemical properties of interest.
Using the combinatorial chemistry technique, one typically begins with a molecule or compound known to be useful. The substance is separated into labeled fragments, often anchoring the pieces to a solid support (e.g., polystyrene beads). Then, using automation, a variety of other molecular fragments are added. This parallel processing quickly produces a vast collection of chemicals that are then stored. By screening the library against a drug target, one can assay any compound or molecule that reacts with a disease target.
Two different combinatorial approaches may be used to generate a large number of compounds for high throughput screening; they are the 1) mix-and-split synthesis approach; and 2) parallel synthesis approach.
Mix-And-Split Synthesis Approach of Combinatorial Chemistry for Drug Development
In the xe2x80x9cmix-and-split synthesisxe2x80x9d approach, compounds are simultaneously created and then the mixture is screened for performance. Reactions occur in the solid phase. The compounds are synthesized on polystyrene beads allowing for very large libraries to be made in a short time. Each bead holds a different pure compound, and each reaction vessel has a mixture of many compounds on separate beads. After a reaction, the beads are split into separate containers, and different agents are added. The beads containing the products of these reactions are mixed then split again and reacted with different reagents. The process is repeated a certain number of times. If activity is found then the compound on the beads causing the activity must be determined. Tags attached to the beads at each step indicate the reagents with which each bead has been treated. After the synthesis is complete, the beads are screened for performance. The chemical structure of the most active compound in the mixture is identified, and this compound is prepared using standard synthetic methods. It is re-synthesized in measurable quantities, purified and then tested. This combinatorial method is best suited for the synthesis of many (up to one million) compounds called a library. The attraction of this combinatorial approach is the speed and cost effectiveness of generating molecular diversity. The challenge is to develop methods to readily identify the active component in a complex mixture either through labeling or statistical methods.
Parallel-Synthesis Approach of Combinatorial Chemistry for Drug Development
In the xe2x80x9cparallel synthesisxe2x80x9d approach, all chemical structure combinations are separately prepared, in parallel, on a given chemical structure (scaffold) using an automated robotic synthesis apparatus. Thousands of vials may be used to perform these reactions, and laboratory robots are programmed to deliver specific reagents to each vial. Although this approach is automated, it often takes longer than the mix-and-split synthesis approach to complete and thus is best suited for the development of smaller chemical libraries.
Biotechnology, pharmaceutical and chemical companies are applying combinatorial chemistry and high throughput synthesis techniques to change the field of chemistry as applied to drug discovery. For drug developers, combinatorial chemistry offers great advantages. It enables a dramatic reduction in development time (four to seven years) by speeding up the synthesis and the identification of lead compounds. In today""s economy, drug competition is heightened by both the agenda set by the present managed-care climate and the drive for inexpensive drugs that become the top choice of healthcare buyers. So, companies are scrambling to create entirely new pharmaceuticals.
At the same time, the Human Genome Project and other gene-hunting efforts are producing DNA sequences for disease-related enzymes and cell receptors. Many of these molecules will ultimately generate successful drugs as chemicals are synthesized that control them. The combinatorial approach is a significant advancement in finding such chemicals-applying the principles of parallel processing to medicinal chemistry.
The introduction of high throughput screening methods in the pharmaceutical industry in the early 1990s produced a fundamental mismatch of skill sets. Medicinal chemists were unable to generate compounds at a pace that fully utilized the capacity of high throughput screening. Today, however, with molecular modeling and combinatorial chemistry, the capacity of high throughput screening is better used. Molecular modeling provides 1) new hypotheses of the mode of drug action, and 2) the identification of key chemical structure features that drug candidates must have. Combinatorial chemistry enables candidate molecules with both desired and ancillary chemical structure features to be rapidly synthesized. And, with combinatorial chemistry the number of molecules that can be made and tested far exceeds the capacity of most high throughput screening.
The drug development process may utilize combinatorial chemistry to create libraries biased towards compounds with desirable properties, such as solubility or a low molecular weight. Such properties make drugs easier for the human body to accept and use. The winning product may come as a complete surprise. At times, a diverse library with as many as 15,000 components is made, out of which a reasonable candidate is selected, then analogs of the candidate are made to find xe2x80x9cthe winner.xe2x80x9d
With combinatorial chemistry and high throughput synthesis, a 10- to 50-fold annual increase in the number of compounds made and tested can be realized. Existing information technologies and business operations, such as compound registration practices and assay result visualization, cannot accommodate this increase. Traditional chemical registration systems may be used for registering discrete compounds associated with the synthetic effort; information systems for the registration and storage of combinatorial chemistry products may also be used. However, it is more popular (but less desirable) to store assay results and related library information within relational databases (e.g., xe2x80x9cOraclexe2x80x9d database) or when no central storage of assay data is available, then the information is saved within desktop programs (e.g., xe2x80x9cExcelxe2x80x9d spreadsheet program). In addition to registration, tracking the synthesis, testing, and heritage of deconvolution products is important.
Synthesis direction includes: 1) combinatorial mixes only, 2) high throughput synthesis only, 3) emphasis on combinatorial mixtures, but high throughput synthesis is pursued, and 4) emphasis on high throughput synthesis, but combinatorial mixtures are pursued.
The intent of combinatorial chemistry efforts includes: 1) lead generation, 2) lead optimization, and 3) combinatorial mixtures for lead generation and high throughput synthesis for lead optimization. Combinatorial chemistry is not exclusively used for lead generation. Other synthetic efforts include: 1) the use of known solution phase chemistry, 2) the use of solid phase chemistry (e.g., peptides, peptoids), and 3) the development of solid phase organic synthesis (SPOS) for novel, non-oligomeric compounds.
From a list of candidate compounds, the compounds are tested for their effects on organisms. Ultimately, the best candidate compounds are tested on humans. However, there is a high failure rate associated with this animal/vertebrate/human testing and it is very time consuming.
Conventional Experimental Clinical Drug Trials
Experimental drugs are administered in clinical trials in attempts to assess their efficacy on a disease, disease state, affliction, ailment, or health/medical condition. Along with a control, the drug is administered to a group of people/animals. An assessment is made as to the drug""s efficacy by observing the disease""s progression or regression. In some instances this observation is straightforward, but typically it has not been. Furthermore, the observation and assessment has been outcome based which adds to the time for analysis.
For example, a clinical research study may be organized to assess the efficacy of a baldness remedy. The test remedy, for instance a pill that is ingested, may be selected from a group of candidate treatments thought likely to be effective. The test remedy may be administered to a group along with a control group receiving a placebo. Periodically, hair-counts are taken on the members of the test study. The remedy""s effectiveness is determined by changes in the hair count. Consequently, outcome assessment is not difficult. However, the study provides minimal information on the mechanisms of treatment. Suppose the outcome concluded that the test remedy was effective in 10% of the group. Did only the 10% have elevated levels of the ingested chemical in their scalp? If so, maybe a better drug delivery system is needed. Did 100% exhibit sufficiently elevated levels of the chemical in their scalp but only 10% possess a naturally occurring biochemical that is known to be easily regulated pharmacologically? If so, maybe 100% success could have been achieved by artificially bolstering the biochemical. The described outcome-based approach provides no direct answers to these questions.
In light of the above, there is a need in the art for a method and system that can enhance the drug development process through real-time in vivo chemical analysis which, in turn, will decrease the amount of time for tracking the effects that drugs have on organisms. A further need exists in the art to ascertain, in real-time, the presence and quantity of applied chemicals on living tissue.
Therefore, a need in the art exists for a method and system for stabilizing reflected light that is fed into a dispersive light processing unit such that real-time in vivo chemical analysis can be provided. An additional need in the art exists for a method and system for stabilizing reflected light that facilitates accurate and rapid tracking of effects that drugs have on organisms.
The present invention solves the problems of collected reflected light for instruments by providing a light stabilizing interface linked to a collection wave guides for combining and stabilizing reflected light into a substantially even spatial distribution of light energy with a substantially uniform light intensity. Even spatial distribution and uniform intensity of reflected light energy are desirable qualities and enhance light measurement techniques such as Ramon spectroscopy.
The stabilization and substantially even spatial distribution of reflected light can be accomplished by a mixing and transmitting device comprising a single optical fiber and optical junction wave guides in the form of optical fibers having a smaller diameter relative to the mixing and transmitting device. The optical junction wave guides are shaped into a linear array in order to maximize the light fed into an input interface of a light processing unit that has a predefined geometrical configuration (usually a slit). The junction wave guides enhance the coupling between the collection wave guides and light processing unit by increasing the spatial resolution of the light energy propagating therethrough. Further, the junction optical waveguides can be sized such that the numerical aperture of the linear array is optimally matched to the light acceptance characteristics of the light processing unit. The light processing unit can be a xe2x80x9cfastxe2x80x9d spectrograph that accepts high numerical aperture fibers, which in turn, increases light processing efficiency.
For another aspect of the present invention, the stabilization and substantially even spatial distribution of reflected light can be accomplished by a single, integral device that includes a collection wave guide matching section and a transition region. The transition region terminates in a shaped end region that is designed to substantially match the geometry of the input interface of the light processing unit. For example, the shaped end region can have a substantially rectangular shape to match to the substantially rectangular shape of the input interface. The total surface area of the transition region can be designed to remain constant relative to the collection wave guide matching section. The light stabilizing interface can substantially reduce light energy loss due to the reduced number of interfaces between the collection waveguides and light processing unit.
In another aspect of the present invention, a method and system for stabilizing reflected light can enhance the drug development process by providing real-time in-vivo chemical analysis of the interactions between drugs and living tissue. This supports an accurate detection of chemical composition and quantity in living tissue. This real-time chemical detection is possible with a light management system of the present invention that can be inserted into or adjacent to an organism.
That the present invention improves over the drawbacks of the prior art and accomplishes the objects of the invention will become apparent from the detailed description of the illustrative embodiments to follow.